The present invention relates to a flight control system, and more particularly to control of a swashplate trajectory.
Control of a rotary-wing aircraft is affected by varying the pitch of the rotor blades individually as the rotor rotates and by varying the pitch of all of the blades together. These are known respectively as cyclic and collective pitch control. Blade pitch control of a rotary wing aircraft main rotor is typically achieved through a swashplate.
The swashplate is typically concentrically mounted about the rotor shaft. The swashplate generally includes two rings connected by a series of bearings with one ring connected to the airframe (stationary swashplate), and the other ring connected to the rotor hub (rotating swashplate). The rotating ring is connected to the rotor hub through a pivoted link device typically referred to as “scissors”, with the static ring similarly connected to the airframe. The rotating swashplate rotates relative the stationary swashplate. Apart from rotary motion, the stationary and rotating swashplate otherwise move as a unitary component. Cyclic control is achieved by tilting the swashplate relative to a rotor shaft and collective control is achieved by translating the swashplate along the rotor shaft.
Pitch control rods mounted between the main rotor blades and the rotating swashplate transfer loads between the swashplate and the main rotor blades. Main rotor servos extend between and attach to the stationary swashplate and the aircraft fuselage. Displacement of the main rotor servos results in displacement of the stationary swashplate. Hence, by actuating selected main rotor servos, collective and cyclic commands are transferred to the rotor head as vertical and/or tilting displacement of the swashplates.
Certain limits may be required for the swashplate linkages to operate properly. Typically, the more compact the swashplate, the more complicated the linkage geometry and the greater the number of linkages required to achieve a desired range of motion. Main rotor servo limits may be required to avoid interference relationships within the range of motion.
Main rotor servo rate limits may also prevent exceedences of a hydraulic system capability which drives the main rotor servos. Since a swashplate requires a combination of servo movements to achieve the desired position, individual limitation of servo rates may result in an undesirable trajectory which produces an off-axis response.